The term "banknote intaglio printing" as used in this specification, is intended to define the type of intaglio printing commonly used to print documents of value and security papers such as banknotes, travelers checks, etc. In that type of printing, the image to be printed is formed in a printing plate by recesses, which may take the form of either dots or lines, and typically include straight and curved lines longer than 1 mm. (0.39 in.). The recesses vary in depth from 0.0005" to 0.010", and are first filled with ink. The paper is then forced into the recesses and a substantial thickness of ink is built up on the paper, i.e., from 0.0005" to 0.005". This type of printing is carried out with an ink having a viscosity of 50-500 poises at 20.degree. C. The ink is usually heated and worked by a train of rollers to reduce its viscosity before it is applied to the printing plate. It adheres to the plate and to the bottoms of the recesses because of its viscous quality. After being applied to the plate, the excess ink on the surface between the recesses is removed either by a scraper blade and by one or more polishing webs of burlap or absorbent paper, or both. The paper to be printed is then pressed between the inked and polished plate and a pressure roller which is held against the plate with a force (commonly termed a "pressure") of 2000-8000 lbs. per lineal inch.
Other types of intagilo printing, such as those known as "photogravure" or "rotogravure", sometimes shortened to "gravure", use ink-receiving recesses in the form of dots with a surface area of less than 1 square mm. and which approximate circles, although they may be somewhat irregular in contour. They vary in depth up to 0.001". The ink vehicles used are highly volatile and have a viscosity of 1-5 poises at 20.degree. C., and hence are readily flowable. They are applied by flooding the plate with liquid ink. The excess ink between the recesses is removed by a single doctor blade. The printing force is in the range from 20-200 lbs. per lineal inch.
The term "doctor blade", as used herein, defines a blade which makes an acute angle with that part of the cylindrical plate surface which is approaching the line of contact with the blade. The term "scraper blade" is used to define a blade which makes an acute angle with that part of the cylindrical plate surface which is receding from the line of contact with the blade.